The invention relates to an arrangement for calibrating a network analyzer for on-wafer measurement at integrated microwave circuits on a metallic base plate of a wafer measurement installation using calibration standards constructed in coplanar line technology on a calibration substrate.
In the manufacture of integrated microwave circuits on semiconductor wafers, the circuits must often be electrically measured even before the division of the wafer (on-wafer measurement). For this purpose, special wafer measurement means (wafer samplers) are known, which have a metallic base plate (chuck) having vacuum openings distributed over the surface, which are connected with a partial vacuum means. The wafer is thus held on this flat base plate by a partial vacuum. Above the base plate, mounts are provided for measurement prods, and measurement points on the clamped-on wafer selected in this way can be driven and contacted by means of precise displacement of the base plate in the X, Y and Z direction (see e.g. the data sheet for the wafer samplers PA200HF or PM5HF of the Su.beta. company, or measurement prods according to U.S. Pat. No. 4,871,964).
For on-wafer measurements of this sort at microwave circuits, vectorial network analyzers are used, in which what is known as a system error correction is required before a measurement. Calibration measurements are carried out according to known calibration methods at several calibration standards whose electrical characteristic quantities are known in whole or in part. Correction data is obtained from these measurements via specific computing methods, which data is subsequently taken into account in the actual object measurement for error correction (e.g. see U.S. Pat. No. 4,982,164).
For the calibration of such network analyzers for on-wafer measurement, calibration standards have proven useful that are fashioned in coplanar line technology, e.g. as a coplanar line, a coplanar double-band line or an asymmetrical coplanar lie on a calibration substrate (coplanar striplines e.g. according to Zinke/Brunswick, Hochfrequenztechnik 1, 5.sup.th ed., p. 157 or 169-176). Coplanar striplines have low dispersion and have, over a large bandwidth, a small change in the wave resistance, as well as a low frequency dependence of the electrical length. Such calibration standards in coplanar stripline technology are for example manufactured on a substrate from sapphire or aluminum oxide in thin film technology. A calibration standard particularly suited for such purposes, as offered for example by the Rosenberger company (calibration substrate RCPW-LMR in produce publication TI 020/18.04.96/E1.0) uses two short coplanar stripline segments (LL) formed on a calibration substrate, with a known characteristic impedance and two short-circuit beams (R). Before the actual on-wafer object measurement, this calibration substrate is set on the base plate of the wafer measurement means, and by means of the measurement prods, which are connected with the network analyzer, the mentioned calibration measurements, e.g., according to the LLR method, are carried out successively at the calibration standards L, L and R.
In microwave circuits fashioned on semiconductor substrates (wafers), only a small part of the substrate thickness (about 500 .mu.m) up to a depth of about 10 .mu.m has an influence on the electrical behavior of the circuit. The measurement results in on-wafer measurement are thus not adversely affected by the metallic base plate during the actual object measurement. However, it has turned out that in calibration measurement, considerable measurement errors occur especially at higher frequencies in the GHz range, during measurement of the calibration standard constructed in coplanar line technology. As a consequence correction errors occur during object measurement.